The invention relates in general to an electrically initiated igniter system to ignite the main propellant in the chamber of a gun. More specifically, the invention provides a electrically initiated distributed igniter that includes an array of igniter pads placed in contact with the main propellant, wherein the igniter pads utilize an integrated oxidizer layer.
Utilizing pyrotechnic igniters and electro-thermal chemical (ETC) planar igniters to ignite the main propellant in the chamber of a large diameter gun is well known in the art. Two of the problems inherent to these conventional igniter systems are delayed ignition of the main propellant and large electrical energy requirements to fire the igniters.
Delayed ignition is a problem during a base ignition of a cartridge with a high loading density is in excess of 1 g/cc. Since the pressure in the gun chamber due to the igniter is rapidly equilibrated, propellant flame spread is the primary ignition mechanism for much of the charge surface. Under these conditions, this is a relatively slow and incomplete process resulting in ignition delays, particularly from one end of the charge to the other.
Very large diameter charges, such as employed in the Navy""s 5-inch Mk-45 gun, also experience the delayed ignition problem. The Mk-45 utilizes a center core igniter and the main propellant charge is thirty-two inches long. Due to its length, this igniter induces ignition time delays in excess of 0.5 ms between the breech and projectile end of the charge. This delay is due to a combination of the detonation cord run up of fifteen inches within the igniter itself and the additional fifteen inches or so of axial flame spread that must occur before the propellant at the front of the thirty-two inch long charge is ignited.
In order to overcome the problem of delayed ignition, it would be desirable to provide a plurality of igniters distributed throughout the charge. Conventional ETC igniters, however, use between 0.25 kJ and 1 kJ of electrical energy per igniter because that energy must drive the main propellant directly, partly through a strongly radiating about 1 eV arc and partly through the convection energy transport of metal/insulator vapor to the propellant. Accordingly, the number of igniters that can be provided is limited due to the energy available in conventional 24 volt firing circuits.
In view of the above, it is an object of the invention to provide an improved igniter system for the main propellant of guns that avoids problems associated with delayed ignition while having a low ignition energy requirement that can be met by conventional firing circuits.
The present invention provides a electrically initiated distributed igniter (EIDI) system that combines most of the advantages of conventional pyrotechnic igniters with those of ETC planar igniters without the disadvantages of either. The EIDI system lends itself to precise timing control of multiple electric circuits, embedded charge ignition, and other design advantages to be discussed here.
A typical EIDI design in accordance with the invention for a large diameter gun might distribute the energy of a conventional base igniter over 1,000 discrete locations and initiate them all with {fraction (1/10,000)} the ignition energy that current ETC systems require. The EIDI system utilizes discrete igniter pads that require only a few millijoules of energy each and are quite small in size, about 3 mm in diameter. As a result, the igniter pads can be used in very large numbers to give good spatial distribution, even for smaller 25 to 40 mm diameter gun charge designs. Energy requirements are so minimal that small disposable firing capacitors and semi-conductor switches can be pre-packaged inside the casing along with the propellant and igniters. This allows multiple igniter firing circuits, used to control the explosion of the main propellant, to be reliably packaged with the charge and firing information, which is energized via a single breech connection. Also related to the low energy requirements of this concept, power requirements are small enough to be delivered by the same 24 v dc firing circuit which is already in place on most modern gun systems.
The basic differences between conventional ETC igniters and EIDI are the total amount of electrical energy required for operation, and the practical limit on the number of individual ignition pads employed. The EIDI system utilizes a primary igniter propellant stage and a secondary main propellant stage. Because an EIDI igniter pad utilizes a primary propellant stage, the energy requirements for ignition of the igniter pade are extremely low, between 0.1 and 10 mJ per igniter pad. In contrast, conventional ETC igniters use between 0.25 kJ and 1 kJ of electrical energy per igniter pad because that energy must drive the main propellant directly, partly through a strongly radiating about 1 eV arc and partly through the convection energy transported to metal/insulator vapor to the propellant.
The EIDI offers several advantages not available with ETC designs. Because the energy requirements are so very small, much of the electrical circuitry can be pre-packaged inside the casing. The firing circuits are disposable and their components include capacitors, switches, and igniter pads. This minimizes external electrical problems by confining them to a power supply and a trigger signal. It also allows an additional degree of flexibility inside the casing by making use of multiple firing circuits to control and modify gas generation rate according to external inputs, for example temperature, projectile weight, and range.